1. Field of the Invention
Heated processing zones that rely substantially on steam have a variety of industrial and commercial applications. The use of steam as a heating source provides a source of high thermal mass heat due to the enthalpy of vaporization of steam. Once the steam condenses, a source of moisture also becomes available. Although heated processing zones can be used to impart desired moisture content to items in the tunnel, such as wood and tobacco, the heated processing zone described herein is intended to impart heat energy to shrink thermo-shrinkable materials that have been pre-applied to containers which then pass through the heat tunnel.
2. Prior Art Statement
The use of shrinkable plastic film for wrapping and over wrapping consumer or industrial products is well known. In addition to acting as a tamper evident indication, such shrinkable films may also be used to fasten two or more articles together. Continuous flattened tubes of thermo-shrinkable material intended to be sectioned into sleeves and place on containers are commonly referred to as shrink band. Shrink band may be constructed of any suitable transparent or opaque film which can be adequately shrunk onto a container in order to produce a form fitting jacket.
The majority of applications within the packaging industry rely on thermo-shrinkable plastic film. The preferred materials are polyvinylchloride (PVC) and polyethylene terepthtalate, (PET). These plastic films typically exhibit shrinkages of approximately 50% along a first axis and approximately 10% along an axis 90 degrees to the first axis. A variation of PET referred to as PTEG, and oriented polystyrene (OPS), have been formulated to provide additional shrinkage up to approximately 70% along at least one axis. The aforementioned shrink band materials tend to shrink at temperatures ranging from approximately 200 degrees Fahrenheit to approximately 350 degrees Fahrenheit. Shrink band materials exhibiting shrinking temperatures outside this range may exist for other applications. Shrink band is formulated to effect a required reduction in geometry in less time than it takes to have the product be compromised from the effects of the shrink-inducing heat energy.
As previously mentioned, the term generally used in the packaging industry for this group of materials is shrink band. The cut sections of shrink band material are referred to as sleeves. Where the coverage of the container is substantial, the sleeves are referred to as body bands or sleeves. If the coverage of the container is substantially around the upper portion of the container, the sleeves are referred to as neck bands. In either of the above mentioned cases, a portion of the shrink band material may or may not cover or may partially cover a cap or seal at the filling or discharge opening of the container.
The shrink band material may be in direct contact with the enclosed product or it may be used as an over-wrap to another containment scheme for the product. The shrink band may also be part of a securing scheme that is intended to substantially maintain product integrity and to assist in preventing the product being intentionally compromised or accidently compromised. Where required, the band material may also contribute to the prevention of product exposure or overexposure to undesired elements including but not limited to air, dust, germs and various frequencies of the electromagnetic spectrum such as visible light and ultraviolet radiation.
The shrink band material may be pre-printed with graphic data, human readable data or machine readable data identifying the enclosed product and including information pertaining to said product and its proper usage.
A further application of the thermo-shrinkable process would include items placed over a section of suitable support material such as cardboard or pre-printed cardboard, or other suitable material that may or may not be pre-printed. The pre-printed material may include graphic data, human readable data or machine readable data.
The thermo-sensitive material is shrunk over the product and said suitable support material. The aforementioned process would typically be used instead of “blister” style packaging where it was desirable to restrict free movement of the contained product or to reduce the ease with which the product could be intentionally or accidently removed from the packaging.
Pre-printed thermo-sensitive materials can replace the need for labels. The pre-printed materials may also perform a decorative function. Based on the type of thermo-shrinkable material being shrunk, the device featuring the heated processing zone, often referred to as a heat tunnel, is constructed in varying lengths accommodating the required heating time exposure of the thermo-shrinkable material. The number of shrink events required per minute and the conveyor speed may affect the time the thermo-shrinkable material is actually inside the heat tunnel, and thus also contributes to the working length of the tunnel.
Typical heat sources of heat tunnels include electric heating elements, infrared emitters and steam sources. Each of these aforementioned systems may feature preferred characteristics particular to their application. Where containers to be jacketed exhibit novel geometries, the preferred advantages of steam-based heating are particularly advantageous at producing predictable and controlled shrinkage of the thermo-shrinkable material.
U.S. Pat. No. 6,958,178, Hayakawa, et al., granted Oct. 25, 2005, ‘Heat-shrinkable polyester film roll,’ extols the advantages of steam a as heat source over that of ordinary hot air when used to heat shrink band material. In the ‘background art’ section, we note:
“(I)ncidentally, for wrapping bottles by heat-shrinkable films, the heat-shrinkable films are hitherto first printed (in printing step) and then processed into the shape suitable for loading onto the containers such as labels (tubular labels), tubes, bags, and the like. Subsequently, these processed films are loaded onto the bottles, which are transferred on a conveyor belt through a heating tunnel (shrinkage tunnel), and the films are tightly bound to the containers by heat shrinkage. Steam tunnels, wherein the films are allowed to shrink by blowing steam, and hot-air tunnels, wherein the films are shrunk by blowing heated air, and the like are commonly used as the shrinkage tunnels.
“The steam tunnels are generally better in heat transfer efficiency than the hot-air tunnels, and thus allow more uniform heat shrinkage of such labels and provide shrunk products better in appearance. However, even if the steam tunnel is employed, the heat-shrinkable polyester films are often not quite satisfactory from the viewpoint of product appearance property after heat shrinkage, compared to polyvinyl chloride and polystyrene films.
“Further, the hot-air tunnel has a tendency to cause large variation in temperature during heat shrinkage than the steam tunnel. Thus, when polyester films, lower in the product appearance property after heat shrinkage than polyvinyl chloride and polystyrene films, are heat-shrunk therein, the resulting films often have whitening due to shrinkage, shrinkage shading, crinkling, deformation, and the like, and especially a problem in appearance due to whitening.”
It becomes readily apparent from reading of Hayakawa, et al., that appearance is a critical issue with heat-shrinkable films, especially in hot air tunnels but appearance is not entirely satisfied when passed through a saturated steam tunnel. Thus, higher heat transfer rates are required to ensure satisfactory appearance of the heat-shrunk packaging material.
U.S. Pat. No. 3,750,303, Gates, et al., granted Aug. 7, 1973, ‘Steam tunnels for treating logs and methods of treatment,’ discloses a multi-zone steam tunnel where “(T)he steam supplied to all zones is modulated for each zone by a temperature regulating valve, each zone having its own valve, which is controlled by an electrical temperature sensing device that operates in accordance with the temperature of the condensate leaving the respective zones, and the atmospheric temperature in the respective zones. While each zone has a separate temperature control valve, steam for all four zones of each tunnel is preferably supplied from a single source.”
This patent introduces steam and condensate into a tunnel in an attempt to maintain a particular humidity as logs are exposed to the combined effects of the steam and the condensate. In this configuration, the steam would quickly lose its heat energy as it is absorbed to warm the simultaneously injected condensate.
Neither U.S. Pat. No. 6,958,178, Hayakawa, et al., nor U.S. Pat. No. 3,750,303, Gates, et al., disclose, suggest or infer the use of a second heat source acting cooperatively with a preferred first heat source to slow the loss of the preferred high thermal mass steam. In addition, neither teach the use of superheated steam for shrinking shrink band material around products or product containers.
Worline, U.S. Pat. No. 3,678,244, issued on 18 Jul. 1972 teaches an apparatus for shrinking low shrink films such as Saran or Polyethylene film around packaged food products using hot water maintained in a range from 190° F. to 210° F. Worline teaches a plurality of atomizing nozzles positioned in the tunnel over the grid or rod belt, and as shown clearly in the drawings, the nozzles are in a single plane and disposed well above the grid. Additionally, Worline employs nine 1.35 Kw pan heaters and nine 1.35 Kw convection heaters to maintain the hot water in the specified temperature range and more specifically “ . . . to form a dense hot vapor or steam cloud that will completely surround the product . . . ” A dense hot vapor or steam cloud is layman's language for saturated steam containing water at temperatures at or below the boiling point of water. Hayakawa, et al, teaches that higher temperature shrink films such as polyester, polyvinyl chloride or polystyrene, when exposed to water, are subject to whitening due to shrinkage, shrinkage shading, crinkling, deformation in low temperature shrinkage tunnels and therefore atomization of water, implying employment of water droplets as taught by Worline, may be acceptable for low temperature shrink films, but is not acceptable for high temperature films used in controlled wrapping of products or product containers and thus will result in poor product appearance when used for shrink band on product containers or directly upon products such as card stock. The 18 heaters of Worline are sufficient to maintain the specified temperature range, however, are insufficient to raise the temperature of the water to boiling at 212° F. and thus are also incapable of producing any higher temperature in the presence of the hot water spray. Though Worline has a shut off thermostat set at 240° F., it is only functional when water flow has stopped. Obviously therefore, Worline does not teach use of higher temperature steam, and in particular, does not teach use of superheated steam for shrink band.
U.S. Pat. No. 6,576,872 B2, issued on 10 Jun. 1003 to Bertero, teaches use of superheated steam for vulcanization of pre-formed elastomeric articles, particularly tubes, such as radiator hoses. Bertero teaches that all the steam is superheated as “(T)he re-circulation circuit . . . is provided with a set of electrical resistors . . . to superheat the steam before it is admitted into the curing chamber.” (Emphasis added) Thus, in Bertero, all the steam is at the same temperature when it enters the chamber as the steam generator and the superheating re-circulation chamber are both external of the apparatus. Bertero does not teach maintaining the temperature of the superheated steam within the chamber by employing heaters in the chamber and as Bertero uses only superheated steam, Bertero also does not teach maintaining the temperature of saturated steam within the chamber but rather teaches elevating saturated steam to superheated steam externally of the chamber. Bertero does not teach the employment of electrical (infrared) heating elements within the chamber to not only transfer the heat from steam but also heat in the infrared spectrum. It is readily apparent then that condensation occurs rapidly in both Worline and Bertero and thus the quality issues discussed by Hayakawa, et al., are present in both devices.